The kinetics of lymphocyte turnover in primates is poorly understood. Studies in HIV infected individuals treated with anti retrovirals have been used to predict the turnover rate for CD4+ cells. Studies in mice have incorporated the uptake of bromodeoxyuridine (BrdU) together with surface phenotyping to determine rates of lymphocyte turnover. We have developed a system whereby rhesus macaques are dosed with BrdU via the intraperitoneal or oral routes, and various lymphocyte subsets can be tracked via FACS analysis. Both naive (CD45RA+Leu8+) and memory subsets of CD4+ and CD8+ T cells have been identified in the BrdU labeled subset of cells. Consistent with studies in mice and humans, we observed more rapid turnover of memory than naive T cells. Use of this technique will permit direct measurement of T cell turnover in SIV-infected macaques.